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Testing The Lambda (oxygen) Sensor

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#16 Sprocket


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Posted 22 January 2017 - 11:49 AM

for future reference as its still fresh in my head, chasing a lamba sensor fault yesterday, we found a couple of interesting things.


Engine running, with the crypton ACT, the reading is in millivolts ( 0.001v), the true voltage the lambda sensor outputs. with the sensor disconnected the reading was fixed at 403mv (0.403v). connecting a sensor that was not in the exhaust and sitting freely on the plastic oil filler cap, the sensor tip started to warm up as would be expected (careful, very very hot, burny burny fingers!), but the volt reading remained 403mv. simply placing the body of the sensor onto something bare metal with a ground path the volt reading instantaniously changed to 200mv, a reading consistant with high oxygen content (it is in the air of course), suggesting the grounding of the sensor body is an impotant factor. not sure if this is just a cheapo after market sensor thing, but i would always recommend a little extra money is spent in buying a Bosch part as i've rarely had issues with them other than damge or old age (bit like me )

#17 pete l

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Posted 12 March 2018 - 01:46 PM

If the voltage is stuck low, using a hose pipe clamp, gently pinch the fuel return 'flexi' line (green), momentaraly until the engine note can be heard to alter tone, too much and the engine will stall. This gives a rich condition and the the sensor should read high volts. The lambda sensor is working correctly and the problem lies eslewhere. If the sensor voltage stays low the sensor may be faulty.



Is this correct ? pinching the green return will allow the injectors to inject more fuel making a rich mixture ???????

#18 Mervyn


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Posted 12 March 2018 - 06:46 PM

Pinching the return increases the pressure at the injectors. The injectors don't know what pressure they are running at. They just open for a set amount of time. Higher pressure, more fuel delivered. Within reason the ecu will correct for this. It's just a quick easy way to test for rich lambda


#19 humph


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Posted 09 July 2018 - 01:23 PM

Just wondering if anyone has any thoughts on the lambda reading taken from my car this morning?  


In the first video the car is idling. I took the video because after a 2 hour (100 mile) drive the revs rose, then dropped off and I struggled to keep the car going, it ran rough, seemed rich to an uneducated man like me.


43296935781_7582bf4fca_b.jpgDiagnostic 1 - 09/07/18 


After that I took this one. It's me adjusting the engine speed using the throttlebody, not the car itself. 


28428700887_b1815826d4_b.jpgDiagnostic 2 09/07/18



From what little I know, and I've read every thread I can find on the matter, this sensor seems to be sticking high, rather than fluctuating high/low. Is this the case, or will it stay high like this in certain circumstances?


If the sensor fails is there a default value the car will use? Thought I'd seen one somewhere.  


Finally would the readings be like this if the wiring was knackered,as it was last time, or is this definitely a duff sensor?


I'd appreciate any help given.





Edited by humph, 09 July 2018 - 01:30 PM.

#20 grayclassic


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Posted 19 August 2018 - 09:20 AM

Hi I have just failed the MOT on high HC.
This is a JDM 1997 which is an MPI in all respects except it has an SPI fuel system

I found the red control pipe to the air filter was cracked at the rubber connection. This has ben sorted.

The O2 readings are

Engine not running. 0.8v
Cold tick over 1.7v
Running temp tick over. 0.1 to 0.8 v. Switching very fast
Running temp 2500RPM. 1.7v

What’s the verdict on the Lamda sensor, or is there anything else I should check?
I have a the full set of readings at ignition on, cold tickover warm tick over and 2500rpm

Thanks for any one who can be bothered to read this

Any suggestions,

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